In wars with termites, ants rescue and care for their wounded

These ants invest a lot of energy in caring for their injured comrades.

Deadly battles play out several times a day in the Ivory Coast’s Comoé National Park, leaving wounded behind. The fights break out when hundreds of African Matabele ants march off to raid a nearby termite mound to slaughter termite workers and haul them back to the nest to feed the colony. But termites, with their strong, sharp mandibles, aren’t easy prey, and raiders often get limbs bitten off in the fight.

In the aftermath of a raid, researchers are finding evidence that the ants care for their wounded. The wounded ants secrete a pheromone that calls other returning raiders to carry their injured comrades home. Back at the nest, healthy nest-mates clean the injured ants’ wounds. And the behavior of injured ants even creates a triage system so that only the ants that might actually be saved get rescued.

“It’s only a flesh wound!”

Ants that are only missing a leg or two can generally make the 50-meter trek back to the nest, but their injuries make them more vulnerable to predators, so about a third of injured ants who try to walk home won’t make it. So when nest-mates are nearby, injured ants slow down and even develop a sudden tendency to fall over.

But “after the returning raid column had passed by without helping her, the injured ant immediately started to follow them at a faster pace,” ecologist Erik T. Frank and his colleagues wrote in their paper.

Lightly injured ants make it obvious they need help.

It may look like these ants are just hamming it up in a play for sympathy, but the behavior actually makes sense. Other ants’ eyesight may not be sharp enough to spot an injury, but they can recognize the slow, clumsy movements of an injured nest-mate. And a slower ant has more time to interact with passing nest-mates, which means better odds of getting picked up. Would-be helpers probably have an easier time pinpointing the source of a chemical distress beacon that’s not moving quickly.

When a rescuer touches a lightly injured ant with its antennae, the injured ant folds its remaining legs up in a position similar to a pupa and lies still, making itself easier to carry. But the most severely injured ants, those missing three or more legs, get left behind, in what looks like an uncanny mimicry of the triage human medics perform on battlefields and in disasters.

“It would be wrong to think that the ants are actually making conscious decisions,” Frank told Ars Technica.

Helpers don’t carry their injured nest-mates home out of compassion or loyalty—ants don’t have the cognitive ability to feel those things—instead they do it because chemical cues prompt them to pick up injured ants instead of dead termites. Similarly, said Frank, “The heavily injured ant does not tell the others to ‘leave her behind’ because she knows she won’t be of use anymore.”

Ants only secrete the “help” pheromone once they’ve managed to pull themselves into a standing position, and the injured ants’ reflex is to try to stand. If they succeed, their bodies secrete the pheromone. If not, they don’t. And even when Frank and his colleagues applied the pheromone to severely injured ants, their wild flailing made them too difficult to pick up and carry, so the would-be helpers eventually gave up and walked away.

Severely injured ants resist rescuers.

“It’s actually what fascinates me most about social insects: the ability to have incredibly complex and sophisticated behaviours based on very simple rules and without cognition,” said Frank.

Best care anywhere

Back at the nest, rescued ants get the best medical care available—which means their nest-mates lick the open wounds where their legs used to be.

“The remaining part of the cut limb was held upwards and nest-mates carefully held the injured limb in place with their mandibles and front legs; this allowed them to intensely lick directly into the wound for up to four minutes at a time,” Frank and his colleagues wrote in their paper.

It’s likely that all that licking helps clean dirt out of the open wounds, and the helpful ants may even be applying an antimicrobial substance of some sort. Several ant species secrete such compounds in their saliva, and other ant species have been seen grooming nest-mates to help fight off fungal infections.

Frank plans to spend his post-doctoral research at the University of Lausanne figuring that out, testing various ant glands for antimicrobial or antifungal properties. He also wants to understand how the ants are able to pinpoint the injury—or tell each other where it hurts.

Changes in the injured ants’ cuticle or exoskeleton (a gaping hole, for instance) could indicate an injury to nest-mates, or they may look for hemolymph—the insect version of blood—draining from the wound. That could also be how ants know when to stop licking an injury; when the hemolymph stops flowing, it’s time to stop licking and move on. Frank still needs more data to test those ideas, though.

However treatment works, it’s clearly effective at preventing infection, and that clearly helps ants live to raid another day. Injured ants who didn’t receive care died 80 percent of the time, but when Frank and his colleagues put the injured ants on sterile soil, their mortality rate dropped to 20 percent. But ants that had nest-mates that licked their wounds only died 10 percent of the time.

For the greater good

Natural selection favors this triage, medevac, and wound care behavior not because it benefits individual ants—remember that the worker ants won’t breed in the first place—but because it improves the fitness of the colony. And that, according to Frank, may be why biologists have never observed this kind of behavior in any other animal species. “Treatment of a wound by another individual is much more beneficial in social insects where evolution generally applies on the level of the colony,” he said.

The benefit to the colony comes in the form of reducing the otherwise high cost of hunting tough prey like termites. Frank and his colleagues noticed that about 21 percent of ants on raiding parties were already missing at least one limb, and four- or five-legged ants learn to move almost as quickly as uninjured ants within about 24 hours. That means that rescuing and treating an injured ant puts it back in the fight the next day.

“By saving injured ants, the colony is able to reduce its mortality, i.e. its costs, when hunting dangerous prey like termites. Since these injured ants later on participate again in future fights, the colony does not need to produce new workers to replace them.”

Classical thinking of "resources spent on the sick and weak are wasted" clearly doesn't apply.

My guess is that since these injuries are not genetic, there is no selectivity that can play a role - especially since so much of the colony is involved in the raids and damage will be somewhat random.

Since it looks like the attacks are based on overwhelming numbers, it makes sense that any ant that could participate on a future raid would be a net gain to save, and thus the evolution leading to the indicator signals.

IANAB, I am talking out of my posterior, but it's the explanation that I've filled in to answer the same question for myself.

Not sure if this was an intentional editorial choice or not, but it's nice to see a follow-up to last year's article on the earlier stages of this research, especially since it answered a couple questions I'd had (triage mechanism, for one).

Classical thinking of "resources spent on the sick and weak are wasted" clearly doesn't apply.

I'm not sure quite how you come to that conclusion, given that the ants clearly distinguish between lesser and more severe injuries, and make a judgement based upon both their capabilities as a species to recover/treat their wounded and the future potentiality of those wounded?

It is hard to think of any human civilisation, of any size or time period, where those value judgments have not been, or are not, applied.

Classical thinking of "resources spent on the sick and weak are wasted" clearly doesn't apply.

I'm not sure quite how you come to that conclusion, given that the ants clearly distinguish between lesser and more severe injuries, and make a judgement based upon both their capabilities as a species to recover/treat their wounded and the future potentiality of those wounded?

It is hard to think of any human civilisation, of any size or time period, where those value judgments have not been, or are not, applied.

More than that, the article suggests that is no judgement by the ants. Either they stand and secrete the pheromone or the don't stand and don't secrete. The triage is essentially conducted by biology rather than any active or passive decision making.

Biology in fact is supporting the mentality that "resources spent on the sick or weak are wasted" - those who have the potential to continue contributing to the war machine are brought back to fighting shape. Those who cannot contribute are left to die.

That is amazing! The more stories I read about ants, the more amazed I am. This one and the one from last year (I think it was last year) about a species of ants that develops a symbiotic relationship with a type of plant just blew me away.

Quote:

“It’s actually what fascinates me most about social insects: the ability to have incredibly complex and sophisticated behaviours based on very simple rules and without cognition,” said Frank.

That is really, really cool. That they do all this without the capacity for cognition. Just based on chemical emissions and 'programmed' behaviors.

Classical thinking of "resources spent on the sick and weak are wasted" clearly doesn't apply.

My guess is that since these injuries are not genetic, there is no selectivity that can play a role - especially since so much of the colony is involved in the raids and damage will be somewhat random.

Since it looks like the attacks are based on overwhelming numbers, it makes sense that any ant that could participate on a future raid would be a net gain to save, and thus the evolution leading to the indicator signals.

IANAB, I am talking out of my posterior, but it's the explanation that I've filled in to answer the same question for myself.

While that makes sense, I feel there's a step missing here.

Look at it this way: There's two separate things that had to evolve for this to work. First, the ants have the excrete some pheromone when injured (but no too injured?). Next, ants have to be able to receive that pheromone and have it trigger some response, in this case carrying the ants back to their nest. Nevermind the after-work of cleaning the wounds later on, which is likely more social then biological.

So yeah, there's several things that had to come into play for this to work. All of these need to happen, or there's no change. It's unlikely both evolved at the same time, but on the other hand it's unlikely one gets selected without the other already being present.

Nevermind the after-work of cleaning the wounds later on, which is likely more social then biological.

I think it's still biological - the article mentions a couple potential mechanisms that would promote that sort of behavior (active bleeding from the stump, for instance) without requiring a social response.

Classical thinking of "resources spent on the sick and weak are wasted" clearly doesn't apply.

It could simply be this cost is only a fraction of the one spent on a new born until it becomes a soldier. Carrying another ant then licking its wound for a few minute is not really expensive if it’s ready for the next raid.

Classical thinking of "resources spent on the sick and weak are wasted" clearly doesn't apply.

My guess is that since these injuries are not genetic, there is no selectivity that can play a role - especially since so much of the colony is involved in the raids and damage will be somewhat random.

Since it looks like the attacks are based on overwhelming numbers, it makes sense that any ant that could participate on a future raid would be a net gain to save, and thus the evolution leading to the indicator signals.

IANAB, I am talking out of my posterior, but it's the explanation that I've filled in to answer the same question for myself.

While that makes sense, I feel there's a step missing here.

Look at it this way: There's two separate things that had to evolve for this to work. First, the ants have the excrete some pheromone when injured (but no too injured?). Next, ants have to be able to receive that pheromone and have it trigger some response, in this case carrying the ants back to their nest. Nevermind the after-work of cleaning the wounds later on, which is likely more social then biological.

So yeah, there's several things that had to come into play for this to work. All of these need to happen, or there's no change. It's unlikely both evolved at the same time, but on the other hand it's unlikely one gets selected without the other already being present.

So yeah, evolution is weird.

I don’t think it’s that hard. It could have evolved from trophallaxis or mutual grooming.

“It would be wrong to think that the ants are actually making conscious decisions,” Frank told Ars Technica.

Individually, probably not. But as a hive mind, yes, these ants have somehow figured out that caring for their wounded is better for the hive. It's doubtful that they thought it through in the same way we might have but the end result is the same.

When we observe these qualities in the natural world, it seems that altruism is built into the universe as a survival tactic, and not just for higher species such as homo sapiens. Fascinating, just fascinating.

Uninjured ants who didn’t receive care died 80 percent of the time, but when Frank and his colleagues put the injured ants on sterile soil, their mortality rate dropped to 20 percent. But ants that had nest-mates that licked their wounds only died 10 percent of the time.

Classical thinking of "resources spent on the sick and weak are wasted" clearly doesn't apply.

My guess is that since these injuries are not genetic, there is no selectivity that can play a role - especially since so much of the colony is involved in the raids and damage will be somewhat random.

Since it looks like the attacks are based on overwhelming numbers, it makes sense that any ant that could participate on a future raid would be a net gain to save, and thus the evolution leading to the indicator signals.

IANAB, I am talking out of my posterior, but it's the explanation that I've filled in to answer the same question for myself.

Even an ant that is only 86% effective, can still draw fire for a healthy ant. Frees up a soldier for the meat grinder, so to speak...

“It would be wrong to think that the ants are actually making conscious decisions,” Frank told Ars Technica.

Individually, probably not. But as a hive mind, yes, these ants have somehow figured out that caring for their wounded is better for the hive. It's doubtful that they thought it through in the same way we might have but the end result is the same.

When we observe these qualities in the natural world, it seems that altruism is built into the universe as a survival tactic, and not just for higher species such as homo sapiens. Fascinating, just fascinating.

It does not make the hivemind anything like conscious. The hivemind, for any meaning you may put in, has never figured out anything. Instead, some population found out some altruistic traits, and it happens that in many situations altruism improves fitness.

Something I noticed is that they don't attack the heavily injured sisters, which could be a sound survivalist tactic. It seems they have evolved very powerful hardwired commands that prevent fratricide.

I ve seen yallowjackets attacking, cutting in half and carrying away heavily injured sisters, so this kind of command is obviously not universal.

“It would be wrong to think that the ants are actually making conscious decisions,” Frank told Ars Technica.

Individually, probably not. But as a hive mind, yes, these ants have somehow figured out that caring for their wounded is better for the hive. It's doubtful that they thought it through in the same way we might have but the end result is the same.

When we observe these qualities in the natural world, it seems that altruism is built into the universe as a survival tactic, and not just for higher species such as homo sapiens. Fascinating, just fascinating.

If you reverse it, it's more interesting: Our own altrouistic ideals are echoes of far more primitive survival instincts, evolved and dressed up with rationalism and feelings.